CO[sub 2] laser scattering technique for studying Langmuir turbulence spectra

A 12-channel system for resolving either the [omega] or [ital k] spectra of plasma Langmuir turbulence is developed. The direct detection system is operated with a scattering linewidth of order 100 GHz at scattering angles ranging from 10[sup [minus]1] to 10[sup [minus]3] rad. Stray light rejection of up to 13 orders of magnitude is provided by an ammonia-filled gas cell. It is possible to vary the absorption frequency width from 20 MHz to 5 GHz keeping absorption in the ammonia line center constant. The [omega] and [ital k] spectra of Langmuir turbulence excited in the plasma by a high-current relativistic electron beam are measured via the technique described.